Good point - if you wait till the gun is at your head - well, that's a disadvantage but even then not insurmountable.
I have seen folks in training beat a drawn gun pointed at them. In FOF, I walked through a door (I had to!) to face two folks with drawn guns - in the following melee of movement, I took two peripheral hits but got two COMs.
Of course, that is not guaranteed, nor an indication of my ninja abilities. Just saying, it ain't over till its over.
On the other hand, I was the crook with the drawn gun and the clerk hit me in the noggin. I fell to the ground and then 'shot' his inner thigh repeatedly. 5
38's (Code Eagle) for real in your leg would have been nasty.